The findings also show that the public thinks the massive project, which aims to ship 830,000 barrels of oil a day from Alberta and the northern Great Plains to refineries on the Gulf Coast, will produce significant economic benefits. Eighty-five percent say the pipeline would create a significant number of jobs, with 62 percent saying they “strongly” believed that to be the case.

At the same time, nearly half of those interviewed — 47 percent — say they think Keystone will pose a significant risk to the environment.

That so many Americans back the pipeline, even with environmental risks, highlights the quandary facing President Obama and his top aides as they weigh whether to approve the proposal.

Several poll participants interviewed this week said they are convinced the pipeline represents the safest way to transport the oil the United States needs from a reliable ally, Canada. But a liberal minority — most of whom strongly support the president — said it will deepen the country’s dependence on fossil fuels and exacerbate climate change.

“I’m concerned about the environment, but we also use a lot of oil and we need to transport that oil,” said Laura Dabose, 54, a retiree in Palm City, Fla.. “There’s an inevitability in it. It’s just a matter of finding the right route, and getting people to go along with it.”

Dabose, who used to be a Republican but now votes increasingly for Democrats because she finds the GOP too extreme, said she sees the pipeline as a better alternative to moving the oil by rail.

Support for Keystone is highest among Republicans, with 82 percent backing it. But majorities of independents and Democrats also want it approved, at 65 and 51 percent, respectively. Only self-identified liberal Democrats lean against, 47 percent to 36 percent.

Roger Embray, a former sales marketer who is living on disability in Sacramento, said the pipeline should create “several thousand” jobs and make the United States less dependent on oil from the Mideast.

Perceptions about the pipeline’s economic upside and environmental risk are closely tied to support for its construction. More than seven in 10 of those who perceive a jobs benefit approve of the pipeline, while those who sense environmental risk are divided: 45 percent say the pipeline should be approved, while 43 percent say it should not.

By 53 pecent to 33 percent, those who perceive both significant job creation and environmental danger say it should be approved.

“We need to put more Americans to work,” said Embray, a 54-year old Democrat who added that he remains worried it would lead to the same sort of spill that took place in 1989 when the ­Exxon Valdez ran aground in Alaska. “I just predict similar occur­rences with this development. I worry about my children’s children.”

Ted Fairbanks, 47, a law student and political independent in Santa Cruz, Calif., said the administration should refuse to grant Trans­Canada a permit on the grounds that the project will lead to greater environmental destruction.

“I oppose it because I think we need to begin weaning ourselves from petroleum that devastates Canadian wetlands and other” habitats, he said. “To build a pipeline that will create a couple thousand jobs, and only for a short time, to take oil down to Texas so we can sell it to other places, is really shortsighted. I think we ought to start developing other renewable fuels, particularly biofuels.”

Kate Comegys, a stay-at-home mother in Chicago who used to work on Wall Street, said the 2013 Arkansas spill from an Exxon Mobil pipeline shows that shipping that way poses serious risks as well.

“I don’t feel like anybody’s going to look out for the people whose land this crosses,” said Comegys, 43, who tends to back Democratic candidates despite being a registered Republican. “The heads of these companies don’t have to live with their mistakes.”

It remains unclear how much that public polling will influence the administration’s final permitting decision. The State Department has completed its environmental assessment of the proposal, which concluded that ­the development would not have a major climate impact given current oil prices.

“Bipartisan majorities in Congress and a majority of the American people support moving forward with the Keystone XL pipeline,” Cindy Schild, the American Petroleum Institute’s senior refining and oil sands issues manager, said in a conference call Thursday. “The Obama administration has all the evidence it needs to approve the Keystone XL pipeline without further delay.”

But Bill Burton, a former Obama aide who works as a consultant for the League of Conservation Voters, said the president has shown a willingness to challenge public opinion on issues ranging from the bailout of U.S. auto firms to passage of a landmark health-care law.

“The president has shown his decisions aren’t based in polling data, but in the best possible policy,” Burton said.

The Post-ABC poll was conducted Feb. 27 through Sunday among a random national sample of 1,002 adults, including interviews on land lines and with cellphone-only respondents. The overall margin of sampling error is plus or minus 3.5 percentage points.